This invention relates to satellite mobile communication systems and, more particularly, to the management of spotbeam selection information in satellite mobile communication systems.
Mobile communication systems exist in two basic forms. These forms are terrestrial and satellite. In a terrestrial system a user terminal, such as a mobile phone handset, communicates through the air with a base station in the cell occupied by the user. In a satellite system, the user communicates via a spotbeam from a satellite. In either system the user must acquire service from a particular operator and a respective cell or spotbeam. This is accomplished by searching among available cells in the terrestrial system, or available spotbeams in the satellite system. In a terrestrial system searching is relatively rapid. The radio signals can be acquired very quickly and can be verified quickly. In a satellite system it takes much longer to verify each frequency. This is due to the physical characteristics of satellite mobile communication systems including, for example, low link margin, transmission rate, and configuration of system data.
In a satellite phone system a user terminal is designed to operate to use data which increases the possibility of faster service acquisition. The data is stored in different types of frequency lists which describe primary carriers of the satellite system. The different types of lists might include a list with all primary carriers used by a particular satellite network. There is normally one frequency per spotbeam. This list is broadcast so that user terminals can receive and store the list while operating in a standby mode. Another type of list describes the surrounding spotbeams relative to a spotbeam that a user terminal is camped on. These description lists may include neighbor spotbeams of the same network or satellite, or for spotbeams of a non-serving network or satellite which has overlapping geographical coverage with the serving network. These lists are also broadcast by the network.
How a user terminal uses these lists and other frequency information is subject to the design of the particular user terminal. Nevertheless, in order to acquire service, the user terminal must scan the various lists to find a suitable spotbeam. As mentioned above, this can be a time consuming process.
The present invention is directed to improvements in prior satellite mobile communication systems, but is generally applicable to user terminal operations in complex multi-operator environments.
In accordance with the invention there is described a user terminal used in a satellite mobile communication system which labels frequency lists to improve management of spotbeam selection information in satellite mobile communication systems.
Broadly, there is disclosed herein a user terminal operable to acquire service in a satellite mobile communication network in which plural service providers each communicate via satellite with users on one or more spotbeams each having a select frequency. The user terminal comprises a communication system including a transmitter and a receiver for communicating via a spotbeam. A memory stores frequency information. The frequency information identifies carrier frequencies associated with the spotbeams in the network. The memory further stores identification information identifying a service provider associated with each carrier frequency. A communication controller is operatively associated with the communication system and the memory for selecting a spotbeam carrier frequency to communicate on, the communication controller utilizing identification information to select the spotbeam carrier frequency.
It is a feature of the invention that the memory stores a history list of carrier frequencies recently used by the user terminal, labeled with the identification information for each of the recently used carrier frequencies.
It is another feature of the invention that the memory stores a neighbor list of carrier frequencies to be monitored by the user terminal labeled with the identification information for each of these carrier frequencies to be monitored.
It is a further feature of the invention that the memory stores an active list of carrier frequencies presently used in the network labeled with the identification information for each of these carrier frequencies.
It is still another feature of the invention that the memory stores a pending list of carrier frequencies to be changed to in the network labeled with the identification information for each of these carrier frequencies.
It is still another feature of the invention that the communication controller includes means for triggering a search for a different service provider than a current service provider that searches among carrier frequencies not identified with the current service provider.
It is still a further feature of the invention that the communication controller includes means for triggering a search for a preselect service provider that searches among carrier frequencies identified with the preselect service provider.
It is an additional feature of the invention that the communication controller includes means for triggering a search for a different spotbeam than a current spotbeam that searches among carrier frequencies identified with the service provider associated with the current spotbeam.
In accordance with another aspect of the invention, there is disclosed a user terminal operable to acquire service in a digital satellite mobile communication network in which plural service providers each communicate via satellite with users on one or more spotbeams each having a select frequency. The user terminal includes a communication system including a transmitter and a receiver for communicating via a spotbeam. A memory stores frequency information. The frequency information identifies carrier frequencies associated with the spotbeams in the network and lists of spotbeams in the network. The memory further stores a public satellite mobile network (PSMN) ID associated with each carrier frequency and/or each list. A communication controller is operatively associated with the communication system and the memory for selecting a spotbeam carrier frequency to communicate on, the communication controller utilizing the PSMN ID to select spotbeam carrier frequency.
There is disclosed in accordance with a further aspect of the invention a method of acquiring service on a user terminal operable in a satellite mobile communication network in which plural service providers each communicate via satellite with users on one or more spotbeams each having a select frequency. The method comprises the steps of communicating via a spotbeam with the network, storing frequency information, the frequency information identifying carrier frequencies associated with the spotbeams in the network, and identification information identifying a service provider associated with each carrier frequency, and selecting a spotbeam carrier frequency to communicate on utilizing the identification information to select the spotbeam carrier frequency.
More particularly, the user terminal when initiating a service acquisition process is able to target the searching process to any PSMN, a particular PSMN, a different than the current PSMN, a different than the current spotbeam, etc. In accordance with the invention, all types of frequency information stored in the user terminal is labeled by a corresponding PSMN ID. Both single frequency and frequency lists are labeled in this manner. Any primary carrier frequency stored in a history list of recently used frequencies is associated in memory with the PSMN that the primary carrier belongs to. Any lists of neighbor frequency information is stored with the PSMN that uses these frequencies. For example, clusters of spotbeams which are neighbors to the currently serving spotbeam are stored labeled with the serving PSMN, while clusters of neighbor spotbeams which belong to another satellite or network are stored with the PSMN identity of that satellite or network. Also, any list of complete primary carrier information and any pending changes to it are stored by the user terminal with the PSMN label these carriers belong to.
Further features and advantages of the invention will be readily apparent from the specification and from the drawing.